A shut-off valve is already known from DE-A-41 22 605 in which the sealing element is formed by a spring steel strip bent in a U shape. The two arms of this spring steel strip are fixed with their free ends on the stationary apparatus part, and at least the arm which co-operates with the movable apparatus part extends substantially in the direction of closure of this apparatus part. In this case a stiffening arrangement is provided to retain the arm of the spring steel strip facing the stationary apparatus part.
Such a shut-off valve has several considerable disadvantages. For instance the elongated sealing element is inclined to uncontrolled deformation. Since moreover the working surface of the sealing element which is exposed to the gas pressure is comparatively large, there is a great danger of the sealing element lifting off from the counter-surface under certain operating conditions. Due to the relative arrangement between the sealing element and the movable apparatus part (for example a valve) co-operating with one arm of this sealing element, it is also necessary in this known construction for the sealing zone to be interrupted in the region of the movable apparatus part, which brings with it the danger of leaks in this region.
The aforementioned disadvantages of the known construction are avoided in a generic device according to EU-B-0 340 430. In this construction the sealing element has at least one bend between one of the two gripping rims which extend parallel to one another and a curved sealing zone, the other apparatus part comes into contact with the sealing element in the crest region of the curved sealing zone and the relative movement between both apparatus parts occurs approximately tangentially with respect to this crest region.
In a device of this type uncontrolled deformations of the sealing element can be avoided much better. Since moreover the gas pressure which acts in the direction of lifting off the sealing element finds a substantially smaller working surface in the known construction described above, a reliable seal is ensured even in unfavourable operating circumstances. Finally, it is advantageous that a sealing element of the generic type can be so arranged relative to the movable apparatus part that an uninterrupted sealing zone is also produced in the shaft region of the moving apparatus part.
Certain improvements have proved desirable in the further development of the device according to EU-B-0 340 430.
The sealing element according to EU-B-0 340 430 is often lifted off somewhat from its bearing surface during the relative movement of the two apparatus parts, so that it is subject to bending stress near its fixing point, which can lead to breaking at this point after a certain operating time.
Furthermore, it has been established that when used in gas conduits with high flow speeds such sealing elements are caused to oscillate, which also brings with it undesirable stresses on the fixing point.
The object of the invention, therefore, is to avoid these disadvantages and to construct a device in such a way that the sealing element substantially maintains its position during a relative movement of the apparatus parts and in particular is not lifted off from its bearing surface. Furthermore, disruptive oscillations of the sealing element should also be largely suppressed.